1. Field of the Invention
The present invention relates to a flange fastening section for connecting pipings and a cooling system of the flange fastening section used especially in a thermal power station such as a chemical plant and an electric plant.
2. Related Art
The flange fastening section is provided for connecting two pipings in the chemical plant, a nuclear power station, the thermal power station, a gas turbine and the like. A spiral gasket is accommodated along a circumferential groove in the flange in order to prevent leak of fluid from the flange fastening section and to improve sealing performance.
A problem of the conventional spiral gasket is described with reference to the drawings.
A spiral gasket 102 is accommodated in a flange groove 120 as illustrated in FIG. 12B in many cases in a flange fastening section 112 for connecting steam pipings 113 in a main steam system and a reheat steam system of the thermal power station up to a steam temperature of about 600° C. as illustrated in FIG. 12A. Heat from the steam fluid is transmitted in a direction indicated by an arrow 118.
The spiral gasket 102 has a structure obtained by rolling a filler material and a hoop material together, and expanded graphite and a superalloy material made of nonferrous metal are generally used as materials of the filler material and the hoop material, respectively.
Metallic O-ring 101, C-ring and the like are used as illustrated in FIG. 12C in the gas turbine and the like in addition to the spiral gasket 102. In this case also, the heat from the steam fluid is transmitted in the direction indicated by the arrow 118.
In this case, the sealing performance of the spiral gasket 102 depends on the expanded graphite mainly used as the filler material, and the sealing performance is hardly maintained with other materials.
However, recently, in order to prevent global warming, it is globally attempted to reduce emission of carbon dioxide (CO2), which largely affects the warming. In a thermal power plant and the like also, a high-temperature steam turbine system has been developed in order to reduce the carbon dioxide emission, and the high-temperature system up to a steam temperature of about 750° C. has been discussed.
However, since steam oxidation of the expanded graphite used as the filler material is started at approximately 650° C. or higher, there is a problem that the graphite is burned down at about 750° C., so that this cannot be conventionally used.
There is also a problem that materials of the hoop material of the spiral gasket 102 and the O-ring capable of being used up to such a high-temperature range are limited to an extremely narrow range in terms of strength. Further, even when the materials may be used, it is significantly difficult to obtain the hoop material of the spiral gasket 102 and the O-ring by cutting work from such materials. Further, there is also a problem that plastic deformation such as creep deformation occurs when using a metal material in the high-temperature range and a sealing surface pressure gradually decreases.
The document, which discloses the technology regarding the conventional flange fastening section, is as follows.    Patent Document 1: Japanese Laid-Open Patent Application Publication No. 2007-127178
As described above, conventionally, the expanded graphite cannot be used as the filler material of the gasket embedded in the flange fastening section when realizing the high temperature in the chemical plant and the thermal and nuclear power stations, the materials for the hoop material and the O-ring are limited and the plastic deformation occurs, thereby a problem that the sealing surface pressure decreases arises.